Physicist Anthony J. Leggett has studied normal and superfluid helium liquids and other strongly coupled superfluids, and explained why helium becomes a superfluid when it is exposed to a magnetic field at extreme low temperatures. Superfluidity is a phase of liquid matter characterized by a complete absence of viscosity, which allows superfluids to act bizarrely, flowing upwards out of open containers or circulating endlessly without friction a closed loop. For his contributions to the theory of superconductors and superfluids, he was awarded the Nobel Prize in 2003.

Leggett's areas of research include cuprate superconductivity, low-temperature phenomena, macroscopic quantum systems, phase coherence and superfluidity in very degenerate atomic gases, quantum fluids, quantum measurement theory, statistical physics, and theoretical condensed matter physics. His work has advanced the theoretical understanding of the quantum physics that underlies macroscopic dissipative systems and condensed systems. Born in London, he holds dual citizenship in England and the United States.